The present invention relates to a method and a system for transmitting alarms, particularly, for transmitting alarms of a fault detected in a connection between an area to be monitored and a control and switching system.
For maintaining safety and due to possible unexpected events, buildings and other premises and/or their functions are monitored either all the time or temporarily. Often, property is kept on these premises which one does not want thieves to get their hands on or one wants to prevent the property from being destroyed. Functions, such as heating, that are on the premises can also be monitored. Fire alarms can be used to sound an alarm so that people who are sleeping are woken up by a loud noise. An elderly person can be monitored or he/she may have an alarm with which a connection can be established to an alarm centre. Several alarms or monitoring functions can be interconnected by means of a network.
Thus, the purpose of a safety system is to reveal and give a signal of circumstances that are unusual or dangerous, such as e.g. moving, unauthorised access, breaking of glass, a fire, smoke, high/low water surface level. The location and storage of a boat or vehicle, etc. in a protected area can also be monitored. Monitoring is carried out by different kinds of sensors placed at the object, which sensors register a change and which have a transmitter or they are in connection with the alarm collection place of the object by means of a network.
The transfer of an alarm and a monitoring function to an alarm centre is transmitted through a telephone subscription line and through network elements. A subscriber""s telephone is used to call a pre-determined number in response to a message given by an alarm observation means.
At the alarm centre or where the alarm has gone, the monitoring of the object can be started, e.g. so that the alarm causes a monitoring camera to operate at the object. The picture is transmitted through a telephone network, e.g. ISDN, to a control place, where the reason for the movement can be followed.
More particularly, the use of ISDN is described, e.g. in the WO publication 9702694, where a telephone network, particularly ISDN (Integrated Services Digital Network), is used for transmitting an alarm. An alarm received from an alarm detection unit placed at the object to be monitored is transferred to an alarm centre through a digital data transmission network. When an alarm is given, the telephone number of the caller of the alarm detection unit is transferred, according to the publication, as alarm information through ISDN channel D. The alarm centre uses this number to generate alarm display to the monitored place before a connection is established through ISDN channel B, e.g. as an audio-video connection. A computer connected to a subscriber connection of the monitored place collects alarm information and xe2x80x9cgives an alarmxe2x80x9d by establishing a call to a pre-programmed subscriber connection. A defect is that information about the alarm cannot be obtained if the subscriber line is cut or it short-circuits (intentionally or unintentionally).
In the invention, the properties of the physical layer of an ISDN line are utilised in the implementation of an alarm system and, thus, it is part of the alarm system. With the help of the invention, one both takes safeguards against vandalism and simultaneously monitors the object. According to the invention, no special terminal (computer) is required that indicates an alarm, but the information of a fault is detected in a network. An alarm can be transferred to a pre-determined subscriber connection. When the subscriber line ceases to function, an alarm facility will be activated. One possible solution that can be used is continuous line testing. By using the properties of ISDN line""s physical layer the line testing can be done by monitoring in the telephone centre the current feeding to the ISDN-terminal placed in the area to be monitored from the telephone centre. Alternatively the line testing can be done in addition to the aforementioned monitoring by monitoring in the centre the synchronization between the centre and the terminal . The alarm is detected in the centre by an increase of current feeding to the terminal and possibly detected, in addition to that, by loss of synchronization between the centre and the terminal. The cut-off of the line between the centre and the terminal is detected by the loss of synchronization between the centre and the terminal in the centre. During testing, it would be noticed if the line has been cut off for some reason other than a good cause, i.e. the testing interval can be changed after a fault has been detected for the first time to discover whether the error message is real or only temporary. When it is a question of a temporary fault, an alarm would not be given, i.e. an error message would be discovered to be a false alarm. An error message can be based either on that:
The line has been broken or the line has xe2x80x9cshort-circuitedxe2x80x9d.
Now an alarm system has been invented, where, according to a first aspect of the invention, there is provided an-alarm system comprising a control and switching system, a terminal at an area to be monitored, a first connection between the terminal and the control and switching system, and the control and switching system is arranged to monitor the first connection between the control and switching system and the terminal, characterised in that the first connection comprises a power feed line for feeding power from the control and switching system to the terminal, and the control and switching system is arranged to give an alarm to a pre-determined alarm monitoring system in response to detecting an increase of current over a predetermined threshold value in the power feed line, and according to second aspect of the invention there is provided a method for transferring alarms in an alarm system, the system comprising a connection between a terminal at an area to be monitored and a control and switching system, and the method comprising monitoring the connection between the control and switching system and the terminal, characterised in that the method further comprises detecting current feed in a power feed line of the connection, and giving an alarm to a pre-determined alarm monitoring system in response to detecting an increase of the current over a predetermined threshold value in the power feed line.
The invention provides a simple way to take care of connection control and a way to give an alarm. In addition, an existing ISDN network can be used. The error detector can be an ordinary sensor. A short-circuit can be accomplished by a closing switch. Monitoring devices can be flexibly added to the area to be monitored. In addition, an alarm can be transmitted through different ways to the desired place.